Process for ablating high density vias in flexible substrate

ABSTRACT

A apparatus and process for ablating a matrix of high density vias in a flexible substrate. The apparatus is cantilevered on a horizontal shelf from a partition where it can be rigidly supported. A vacuum container reciprocates towards and away from the partition and supports the horizontal shelf by permitting supporting casters to bear on and be supported by the reciprocating container. When the container is away from the partition, servicing of the apparatus as well as the insertion an removal of substrate can occur. When the container is adjoined to the partition, a vacuum can be drawn on the apparatus and processing commenced. A continuous flexible substrate is provided extending in a circuitous path between a supply roll and a take up roll, all interior of the container. The flexible substrate is maintained under constant tension and incrementally advanced. The substrate is incrementally advanced and stopped, passing across a table. When the roll is advanced, the table releases the substrate and is cleaned of the debris resulting form previous ablations. When the roll is stopped, the table clamps and precisely levels the substrate for sequential ablation of the substrate.

This invention relates to the phase mask machining of thin flexiblelaminates with high density regular patterns of vias. Specifically, anapparatus and process for such high density phase mask machining isdisclosed.

BACKGROUND OF THE INVENTION

Phase mask machining is known. Specifically, coherent light scans amask. The mask is provided with transparent or reflective patterns inthe form of computer generated holograms which alter the phase andamplitude of the coherent light incident upon the mask. The patternsproject working images to a workpiece or substrate which is "machined"by ablation, typically by the placement of apertures such as viasthrough the workpiece.

In MacDonald et al. U.S. Pat. No. 5,362,940 entitled Use of Fresnel ZonePlates for Material Processing issued Nov. 8, 1994, phase mask machiningwas disclosed utilizing so-call subapertures. In this patent, eachsubaperture contained its own image information typically exclusive ofthe remaining subapertures.

In the above patent, each subaperture contains at least two subsectionsof optical information. First, the subaperture contains convergenceinformation. The coherent light when scanning the subaperture comes tofocus at a working distance from the mask. This function can be referredto as focus or convergence and usually takes the concentration of thescanning light from an intensity where no ablation will occur to asubstrate to an intensity where ablation can occur at the substrate.

Second, the subaperture contains image information. Specifically, and byconstructively and destructively interfering the amplitude and phase ofthe rays of coherent light, a working image of tailored intensity can begenerated by the subaperture. By way of example, we have constructedworking images of designed intensity profile which can ablate aperturesof specific shape for the generation of ink jet nozzles.

In the phase mask machining of optical substrates, it is frequentlydesired to place a repetitive patterns, for example rows and columns ofvias, onto a substrate. In many applications, the size of the substrateswhich are required to be patterned or machined exceeds by many times thesize of the area of the mask that can be directly written by aconventional E-beam.

In the fabrication of masks using conventional E-beams, extremely fineresolution patterns for computer generated holograms (CGHs) are writtento small areas--usually less than 5 inches by 5 inches. It is commonthat such small areas must be written in relatively long periods oftime. Even with accelerated techniques of mask writing, it is notuncommon for masks having 50 to 500 million (and up to one billion)features to be written in periods of time exceeding 8₁ -hours with anE-beam.

We have pioneered phase mask machining. We have discovered that it isdesirable to process large substrates with high densities of featuressuch as rows and columns of vias. In this processing, two requirementsmust be met.

First, the features produced on the substrate should have the highestpossible density.

Second, the features produced over a large area should be preciselylocated with respect to one another.

APPLICATIONS NOT PRIOR ART

In an application Ser. No. 08,536,583, filed simultaneously herewith onSep. 29, 1995 and incorporated herein by reference, entitled LargePrecision Masks for Phase Mask Machining, now pending we disclose alarge phase mask for phase mask machining. This mask, which is either ofcomposite or monolithic construction, has a large area preciselyconfigured with optical features for the patterned ablation ofsubstrates below the mask. The large area mask has the advantage ofenabling the maximum density of features such as vias and having thesefeatures precisely located one with respect to another.

In scanning large area plates it is necessary to "stabilize" thescanning coherent light. Since the optical features on the mask areprecisely located one with respect to another, the same registration isdesired when the optical features are projected as working images forthe ablation of a substrate. This requires that the beam in scanning onepart of the large phase mask be parallel to the same beam when scanningall other portions of a large phase mask. If the beam deviates fromparallel as it scans from one portion of the large mask to otherportions of the large mask, the underlying and ablated working imageswill likewise deviate from their intended alignment. Additionally, suchdeviation can change the angularity of the coherent light between themask and the workpiece. This causes the working image produced by thesubaperture to deviate from its intended position. The intended ablationat the workpiece is degraded.

In prior scanning arrangements, it has been possible to achieve paralleltransport of projected coherent light beams (usually laser generated)utilizing air bearing supported stages. In the ablation of large areasubstrates, the use of a vacuum has been found preferable.Unfortunately, air bearings cannot be used in such a vacuum; the airfrom the bearing operates to destroy the vacuum.

In patent application Ser. No. 08/537,079, filed simultaneously herewithon Sep. 29, 1995 and incorporated herein by reference, entitledStabilization of Parallel Transport Mirror System, now, pending we setforth the solution to this problem. Specifically, a beam scanning systemand attached system of beam stabilization is utilized for ensuring theparallel transport of an orthogonally deflected coherent light beamscanned in normal incidence over a planar large area phase mask. A firstscanning stage with right angle reflecting mirror scans the beam in theX-direction and reflects the scanned beam to the Y-direction. A secondscanning stage with right angle reflecting mirror is mounted to thefirst scanning stage. This second scanning stage deflects the scanningbeam in the Y-direction and reflects the beam downward through the largearea mask and onto the workpiece. The scanning beam has divided out asmall portion thereof as a reference beam. This reference beam is thendiverted to precisely opposite orthogonal paths to the incidence of thescanning beam. A first reference stage with right angle reflectingmirror scans the beam opposite to the X-direction of the scanning beamand reflects the reference beam opposite to the Y-direction of thescanning beam. A second reference stage with right angle reflectingmirror is mounted to the first scanning stage. This second referencestage deflects the scanning beam opposite to the Y-direction andreflects the beam upward opposite to Z direction of incidence throughthe large area mask. After upward deflection, the beam is reflected atan optical flat and retro-directed oppositely through the referencepath. After retracing the orthogonal reference legs, the beam isdiverted to a quad detector. Beam excursion at the quad detectormeasures departure from true parallel transport to produce a signal fordriving a single steerable mirror in 2-axis angular deflection onincidence to the scanning system. An alternate but not preferredembodiment is disclosed utilizing reflection of a portion of theincident scanning beam with reflection preferably at the large areaphase mask. Use of an independent reference beam is also disclosed.

This disclosure relates to the resultant tool utilizing the abovedisclosures in combination. A new tool is generated which is capable ofablating large quantities of substrate with high density apertures inthe order of one million vias per square foot of material.

A related patent application is entitled Apparatus and Process for UsingFresnel Zone Plate Array for Processing Materials, Ser. No. 08/121,060filed 14 Sep. 1993, now U.S. Pat. No. 5,481,407 issued Jan. 2, 1996.Similarly, another related patent application is entitled Apparatus andProcess for Highspeed Laminate Processing with Computer GeneratedHolograms, Ser. No. 08/201,600 filed Feb. 2, 1994, now U.S. Pat. No.5,571,429 issued Nov. 6, 1996. In this latter disclosure, ablationoccurs in a vacuum environment.

DISCOVERY

In producing the tool of this invention, we have made severaldiscoveries. Since we are the pioneers of this type of ablation, andsince the prior art does not discuss or consider the difficulties we setforth here, invention is claimed in recognizing these difficulties aswell as designing apparatus for overcoming these difficulties.

First, it is desirable to process the substrate in a vacuum. If thesubstrate is not processed within a vacuum, oxidation of the polyimideoccurs and hydrocarbons are formed. This occurs in the form of soot.Where a vacuum is not utilized, the accumulated soot does not travel farand is immediate to the table and the substrate being processed. Thissoot lands on the substrate being processed. Further, it lands on andadheres to surfaces on which the substrate is processed. This can causethe material being processed to be out of registration with the producedworking images. Further, as the material is incrementally advanced, itis scratched.

Secondly, and since it is highly desirable to process the material in avacuum, the question has arisen of the possibility of placing a windowimmediate overlying the substrate to be ablated. This course has beenrejected. Specifically, large windows inevitably accumulate artifacts.These artifacts become repeatable with respect the substrate as it isprocessed, generating repeatable defects in the repeating patterns ofthe substrate. Therefore, a beam generated outside of the vacuum isscanned inside the vacuum so that artifacts are not repeatably generatedon produced product.

Third, throughput of the invention is extremely important. We havetherefore determined to utilize side-by-side beams. These side-by-sidebeams when both operational increase throughput; when only one beam isoperational, total loss of production capacity of the machine does notoccur, it runs at roughly half speed. Provision can be made foroperation of the disclosed apparatus with one laser.

Fourth, heating in the vicinity of the ablated substrate cannot betolerated. Unfortunately, the ablative process generates heat.Specifically, we have found heating to cause distortion of thesubstrate. This distorts the regular ablated matrix of vias that we aretrying to achieve. Further, the distorted laminate can move from itsposition of precise support on the table.

Finally, and since the entire apparatus and process must be carried outinternally of a vacuum, provision must be made for the convenientsupport of the apparatus within a vacuum container. At the same time,access for servicing of the equipment and suitable adjustment of theoptics is required.

SUMMARY OF THE INVENTION

A apparatus and process for is disclosed for ablating a matrix of highdensity vias in a flexible substrate. The apparatus is cantilevered on ahorizontal shelf from a partition where it can be rigidly supported. Avacuum container reciprocates towards and away from the partition andsupports the horizontal shelf by permitting supporting casters to bearon and be supported by the reciprocating container. When the containeris away from the partition, servicing of the apparatus as well as theinsertion and removal of substrate can occur. When the container isadjoined to the partition, a vacuum can be drawn on the apparatus andprocessing commenced.

A continuous flexible substrate is provided extending in a circuitouspath between a supply roll and a take up roll, all interior of thecontainer. The flexible substrate is maintained under constant tensionand incrementally advanced. The substrate is incrementally advanced andstopped, passing across a table. When the roll is advanced, the tablereleases the substrate and is cleaned of the debris resulting fromprevious ablations. When the roll is stopped, the table clamps andprecisely levels the substrate for sequential ablation.

Windows in the vacuum vessel permit the entry of the externallygenerated laser radiation outside of the vacuum to internal scanningapparatus within the vacuum for permitting ablation of the substrate. Aholographic mask is provided having a multiplicity of holographicsubapertures is provided immediately overlying the substrate. The maskis serially scanned by coherent light across the subapertures. Thesubapertures when scanned produce at a working distance from the mask anarray of working images. The array of working images ablates acorresponding array of vias in the substrate. By repeated sequentialadvance and ablation, entire rolls of substrate can be provided withhigh density matrices of vias.

An advantage of the disclosed process is that radiation incident on thesubstrate which is not focused to ablating intensity has the tertiaryeffect of cleaning the substrate and table of accumulated debris.

A further advantage of the apparatus is that considerable material canbe process once a vacuum is drawn. Specifically, continuous processingof substrate for a period of several hours can occur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, and 1B are a side elevation, and a reduced end elevation of avacuum contained machine for successively advancing web sections andphase mask machining those web sections to produce high densityoptically ablated features;

FIG. 2 is a side elevation section similar to FIG. 1A illustrating themachine for successively advancing web sections withdrawn from thevacuum chamber;

FIG. 3 is a plan view of the beam scanning system of this inventionillustrating the scanning motion of the stabilized beam system with thescanning beam scanning vertically downward and the reference beamscanning vertically upward;

FIG. 4 is a perspective view of the scanning path and the reference beampath for effecting stabilization of the scanning beam in passing througha large area phase mask for ablating high density features on thesuccessively advanced web;

FIG. 5 is a perspective view of the large area phase mask and workpiecefor ablating the webbing with high density images;

FIG. 6 is a schematic of an alternate embodiment illustrating thealternate scheme of stabilization;

FIGS. 7a, 7b are electrical schematics of a circuit for driving thesteerable mirror to maintain parallel transport in all positions of scanover large area phase mask;

FIG. 8 is a side elevation view of the scanning table of this inventionadapted for the parallel transport of two side-by-side beams from pairedand alternating lasers being processed by the scanner;

FIGS. 9A, 9B and 9C are respective side elevation and two end elevationviews of the assembled table; and,

FIG. 10 is an exploded view of the table of this invention foridentifying the discrete parts of this invention and setting forth theiroperative interconnection.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1A and 1B, vacuum chamber C is shown reinforced bysteel beams 14. Internal of vacuum chamber C, there is provided scanningtable S, large mask M, and workpiece W.

Overall operation can be simply described. Coherent light L passesthrough chamber window 16 to scanning table S. At scanning table S,coherent light L is deflected downward and scanned through and acrosslarge mask M. During scanning, large mask M forms a matrix of ablatingimages in workpiece W.

In the case of the present disclosure, workpiece W constitutes flexiblethin film 17 advanced from supply roll 18 to take up roll 20. Advance isconventional and consists of incremental and discrete twelve inchadvances so that large mask M scanned by coherent light L can scanflexible thin film 17 in one square foot sections to place in the thinfilm a matrix of ablated vias (or holes). It will be noted that the pathof flexible thin film 17 is serpentine; this type of path isconventional and adjusted to both the material being processed and theparticular material by standards well understood in the prior art.

It will be observed that the entire apparatus for incrementallyadvancing flexible thin film 17 is here placed within a vacuum. It willbe understood that the stabilizer of this invention could work equallywell with flexible thin film 17 ablation where the film has a vacuumonly placed locally over the film section being ablated. This, however,is not preferred for several reasons.

First, a local window through which the beam would have to be disposedimmediately over flexible thin film 17. This window would have to be atleast as large as large mask M. Such windows are expensive and wouldover time accumulate optical artifacts. The result of these artifactswould be repeated on the processed product.

Referring to FIG. 2, opening of vacuum chamber C is illustrated eitherfor servicing of the apparatus such as withdrawal of processed flexiblethin film 17 and insertion of unprocessed flexible thin film 17.Specifically, vacuum chamber C includes fixed end wall 22. Fixed endwall 22 includes cantilevered platform 24 with outer rollers 26.Likewise, vacuum chamber C is supported on chamber support rollers 28.Once vacuum is broken, vacuum chamber C is rolled outward exposingscanning table S, large mask M, and workpiece W to atmosphere. Withvacuum chamber C, it supports outer rollers 26 and thus assists insupporting cantilevered platform 24. It will additionally be noted thatduring such opening, scanning table S, large mask M, and workpiece W allremain fixed with respect to fixed end wall 22 and coherent light Lthrough chamber window 16. Thus, and when vacuum chamber C is open,alignments of coherent light L with respect to scanning table S, largemask M, and workpiece W can easily be made.

Referring to FIG. 3, a plan view of scanning table S is illustrated.Coherent light L enters through chamber window 16 (not shown) andeventually to steerable mirror 30. As will be understood more fully,steerable mirror 30 is driven responsive to deviations from vertical ofcoherent light L as it leaves scanning table S. Steerable mirror 30 isdriven to cause movement of coherent light L equal and opposite to anyvertical misalignment produced during scanning. By such equal andopposite movement to departures from vertical during scanning ofcoherent light L, exact parallel transport of coherent light L occurs atall positions of scan on large mask M.

In the following discussion, the function of scanning table S will firstbe described. Thereafter, stabilization of the scanned beam with respectto vertical will be set forth.

Regarding scanning of the beam, in incidence through large mask M,coherent light L passes to X-direction reflecting mirror 32, causing thelight to pass parallel to the X-direction of scan. Thereafter, coherentlight L is incident on Y-direction reflecting mirror 34. Stopping here,scan in the X-direction can be understood.

Scanning table S is driven at first stage 36 by motor 38 alongX-direction 37. Thus the point at which Y-direction reflecting mirror 34deflects to the Y-direction 40 causes X-direction 37 scan of coherentlight L.

Scanning in Y-direction 40 is analogous.

Scanning table S is driven at second stage 42 by motor 43 in Y-direction40. This second stage 42 is supported on first stage 36. It thereforemoves in the X direction whenever stage 36 so moves. It has mountedthereto Z-deflection mirror 45. Z-deflection 45 is the same asstabilizing mirror 30. This Z-deflection mirror 45 causes light to beincident straight down on large mask M. The position that Z-deflectionmirror 45 occupies for this downward deflection of coherent light Ldetermines the Y-position on large mask M.

Having set forth the scanning path, reference can now be made to FIG. 5.In this figure, the production of flexible thin film 17 workpiece W withmatrix of vias 46. Coherent light L scans large mask M in X-direction 37and Y-direction 40. In such scan it passes over discrete subaperturesection 48 of large mask M. Presuming verticality, it will producematrix of vias 46 under discrete subaperture section 48.

Now presume that coherent light L has moved on in scan to discretesubaperture section 48'. However, and since the respective first stage36 and second stage 42 are roller bearing supported, slight variance inthe incidence of coherent light L on large mask M has occurred. Asillustrated, the light has departed from true vertical. Two effectsoccur.

First, instead of producing matrix of vias 46' in precise alignment withprevious matrix of vias 46, displacement occurs. Transfer of matrix ofvias to misalignment location 50' occurs.

Second, the so-called "working distance" for the discrete apertures willchange. Presuming that this distance increases, the actual workingimages produced may be other than precisely aligned with workpiece W.

It will be understood that FIG. 5 illustrates the problem in an expandedformat. Understanding the true scale and total magnitude of vias isimportant. Since in a typical area of one square foot it is contemplatedthat one million vias will be located, density of the vias is extremelyhigh. Further, and for many features to be configured on suchsubstrates, precision of alignment of the vias with respect to oneanother is required. Where vias or groups of vias are out of alignment,unacceptable irregularity of the produced substrate occurs. By way ofexample, misalignment location 50 represents such a case. Accordingly,it will be understood that it is necessary to stabilize coherent light Las it scans large mask M.

In many cases it has been possible to use air bearing stages. Suchstages have sufficient precision to allow acceptable parallel transportof coherent light L. However, the reader will understand that thestabilization scheme here utilized will also assist such air bearingstages from having improper alignment to misalignment location 50.

Unfortunately, air bearing stages cannot be considered within vacuumchamber C. Leakage from such air bearing stages would destroy the vacuumthat vacuum chamber C creates. This being the case, the respectivescanning table S at first stage 36 and second stage 42 have to bemounted on roller or other mechanical contact bearing.

We have discovered in the analysis of such mechanical bearing mountsthat only gradual misalignment occurs as a function of scanner position.Such misalignment when graphed with respect to scanning displacementproduces a gradual angular misalignment of scanning beam L. This beingthe case, stabilization of coherent light L can easily occur. What isneeded, is a scheme of determining the misalignment from a referencepath and deriving from the determined misalignment at the reference paththe required correction of the scanning path. Input of that determinedcorrection could then occur to steerable mirror 30.

With respect to FIG. 3 and 4, the reference path can easily beunderstood. First, Y-direction reflecting mirror 34 has slight beamsplitting transparency. It passes reference beam 54 to first referencedeflecting mirror 56 and then to reference beam splitter 58. The sumdeflection of first reference deflecting mirror 56 and reference beamsplitter 58 is to cause reference beam 54 at X-direction reference path60 to proceed opposite to and parallel to scanning coherent light L fromX-direction reflecting mirror 32.

This reference beam 54 then proceeds to second reference deflectingmirror 62 where deflection to Y-direction reference path 64 occurs.Again, this path is opposite to and parallel to scanning coherent lightL from Y-direction reflecting mirror 34.

Finally, reference beam 54 is incident upon Z-deflection referencemirror 66. Deflection at Z-deflection reference mirror 66 causes lightto be deflected upwardly opposite to and parallel to light fromZ-deflection mirror 45.

Thus, the incidence of the reference path of reference beam 54 isunderstood.

Reference beam 54 is incident to optical flat mirror 68 mounted toscanning table S and independent of respective first stage 36 and secondstage 42. Reflection of reference beam 54 occurs.

Reflection occurs to Z-deflection reference mirror 66, Y-directionreference path 64, second reference deflecting mirror 62, X-directionreference path 60 with incidence to first reference beam splitter 58.Like Y-direction reflecting mirror 34, second reference deflectingmirror 58 is partially transparent. It passes light to quad detector Q.

Stopping here, and presuming the misalignment previously alluded to inFIG. 5, it will be understood that reference beam 54 upon incidence toquad detector Q will undergo excursion. That excursion can be turnedinto a signal to drive steerable mirror 30. This can best be understoodwith reference to FIG. 7.

Coherent light L enters system and is split by Y-direction reflectingmirror 34. The minor portion of the beam that passes through Y-directionreflecting mirror 34 is used only for scanner stage stabilization and isreferred to as reference beam 54. This reference beam 54 reflects offmirror first reference deflecting mirror 56 and first reference beamsplitter 58. Reference beam 54 then reflects off Z-deflection referencemirror 66 which is parallel and physically linked with Z-deflectionmirror 45 (see FIGS. 3 and 4).

Upward deflection to optical flat mirror 68 occurs. No matter wherescanning table S is in its range of motion, reference beam 54 reflectsoff optical flat mirror 68 back through first reference beam splitter 58through quad detector focusing lens 70, deflection mirror 71 and finallyquad detector Q.

Quad detector Q is reverse biased by voltage reference 113 and operatesin the photoconductive mode. Photodiode currents are four in number fromthe quad detector, with only one of the four circuits being illustratedhere. These photodiode currents pass through transimpedance amplifiers111 which both amplify and convert the photodiode currents to voltagelevels. The peak voltage level attained during the laser pulse iscaptured by peak detector 112 and buffered at buffers 115 foracquisition by A/D converter 118. The voltage from one of the 4 peakdetectors must be of sufficient amplitude to exceed the thresholdvoltage set by potentiometer 114 which allows comparator 116 to switchstates. The output of this comparator is used to interruptmicrocontroller 119 which initiates A/D conversions on the 4 bufferedquad detector signals. Immediately after the 4 quad detector signalshave been acquired a reset pulse is generated via digital I/O 117. Thereset pulse resets all 4 peak detectors 112 simultaneously by makingthem ready for the next laser pulse.

The acquired quad detector signals are used to generate normalizeddirectional error terms for the X and Y axes. These signal errors aredigitally low pass filtered and converted by a constant to a targetvalue in encoder counts. The difference between the target encoder countand the present encoder count is the error term for a PID control loopthat generates with pulse width values. The pulse widths are fed to a2-axis digital PWM motor driver 121 via digital I/O 120. The motors 122and 123 control the motion of the physically linked scanner mirror 124and steerable mirror 30. The error terms are generated in such fashionas to always steer the stabilizing beam back to the center of the quaddetector, thus correcting for roll and pitch in the scanner stagemotion. When the stabilizing beam is perfectly centered, the signalerrors are zero and the pulse widths sent to the motor driver are zero.

System alignment is manual mode and adjustments to PID parameters can bemade through the remote control and display module 126. This portabledevice can be placed in the immediate vicinity of the optics to allowthe user to both tune and monitor system performance.

With reference to FIG. 6, it should be understood that verticalstabilization can be achieved utilizing light reflected from large maskM. In such a device, the incident and upper surface 130 of large mask Mwould be made reflective to at least a portion of the light incidentupon large mask M. Fresnel reflection from an uncoated mask surface isthe typical reflection mechanism. Thereafter, reflection through thescanning optical train of scanning table S would occur with a beamsplitter and quad detector Q effecting stabilization. In such a case, amirror such as X-direction reflecting mirror 32 would be the site forthe beam splitter and an appropriate quad detector Q would be usedbehind X-direction reflecting mirror 32.

Alternately, reference beam 54 could be generated by an additional lasersource. For example, reference beam 54 could be independently generatedby a helium-neon laser. The reference laser and stabilized beam would beinitially (before going onto scanning table S) moving in the samedirection or at least in fixed directions relative to one another. Whilethe detecting circuitry after quad cell Q would be somewhat different,the arrangement and disposition of optical elements would be the same.The detecting and processing electronics is somewhat simpler and a HeNeor other CW laser is desirable, in fact preferable.

Referring to FIG. 8, optical panel P is shown. Coherent light beam L₁ isincident upon vertical deflecting mirror 132, deflected horizontally atsteerable mirror 134, and through beam expanding Galilean telescopehaving small negative lens 136 and large motorized positive lens 138.Vertical deflection to a combined beam path occurs at verticaldeflecting mirror 140.

Likewise, coherent light beam L₂ is incident upon vertical deflectingmirror 142, deflected horizontally at steerable mirror 144, and throughbeam expanding Galilean telescope having small negative lens 146 andlarge motorized positive lens 148. Vertical deflection to a combinedbeam path occurs at vertical deflecting mirror 150.

Presuming that the beams are parallel, both parallel beams are deflectedat fractional beam splitter 160 with the main energy input of coherentlight beams L₁ -L₂ eventually to steerable mirror 30. Thus presumingthat coherent light beams L₁ -L₂ are precisely parallel, scanning tableS will be fully capable of assuring parallel transport of the resultingbeams.

Referring further to FIG. 8, fractional beam splitter 160 diverts asmall fraction of coherent light beams L₁ -L₂ to horizontal analysiscell mirror 162, through beam analysis beam splitter 166, beam focusbeam splitter 164, to beam pointer deflecting mirror 168. Light isdeflected through Fresnel focusing plate 170 to quad detector Q₁.

Coherent light beams L₁ -L₂ alternate in their respective pulses. Quaddetector Q₁ is switched; driving steerable mirror 134 when coherentlight beam L₁ is active and driving steerable mirror 144 when coherentlight beam L₂ is active. Simple adjustment thus assures that whencoherent light beams L₁ -₂ are incident upon fractional beam splitter160, the respective paired beams are precisely parallel. When the beamsare precisely parallel, incident parallel transport will be assured atscanning table S.

Table T and its function of maintaining the substrate in position forablation can now be set forth. Table T is located immediately below maskM. It functions to permit intermittent advance of polyimide P indirection 137 and to clamp polyimide P during ablation of a matrix ofvias.

Referring to FIGS. 9A, 9B, and 10, table T of this invention can beunderstood with respect to its main operational portions.

Polyimide P passes over front end roller 135 at the lead edge of table Tand rear end roller 136 at the trailing edge of table T. Theserespective rollers serve to flatten polyimide P at the point of passageof the polyimide over the rollers.

At the side edges, polyimide P is threaded over the top of pairedsupport rails 102. The top of these support rails 102, front end roller135, and rear end roller 136 establish the distance of polyimide P frommask M for the ablation of vias.

Table T includes thirteen support/cooling tubes 142 that provide 94% ofthe support of polyimide P as it passes over table T between front endroller 135 and rear end roller 136. These support/cooling tubes 142 arefabricated from aluminum alloy and have water constantly circulatedthrough from manifolds 104 on either side. (See FIG. 9C).

Referring to FIG. 10, support/cooling tubes 142 are independently sprungon each end. The respective support/cooling tubes 142 fit at roundedends 143 in elongate slots 145. Tube carrier 107 and front and rear tubecarrier links 108 together with cooling tube springs 147 causesupport/cooling tubes 142 to be biased upwardly against edge 113 of webedge clamp 114.

It will be observed that each of support/cooling tubes 142 includes flatsurface 144. Flat surface 144 includes several functions. First, whenthe respective flat surface 144 of all tubes are registered one toanother, a support surface is defined which supports approximate 94% ofthe surface of the material being ablated. Second, when support/coolingtubes 142 are rotated, flat surface 144 is able to dump debris createdduring ablation. Absence of this debris enables following ablations tooccur without either scratching or interference in substrate elevationfrom the accumulated debris. Finally, this surface enables the heat ofablation to be conducted to the tubes which in turn are water cooled.

Clamping of polyimide P to support rail 102 occurs through web edgeclamp 114. Web edge clamp 114 has edge 113 which overhangs and extendsbeyond support rail 102. Edge clamp spring 129 urges web edge clamp 114down onto support rail 102 to clamp the substrate. Edge clamp blocks 109serve to coact with front bell crank 112 and rear bell crank 133Support/cooling tubes 142 are thus free to seek their own level againstthe bottom of the overhanging edge of the web edge clamp (see 9B)ensuring accurate location in relation to the web and the edge clamp.Web edge clamp 114 un-clamps at the end of the opening cycle and clampsat the beginning of the close cycle. Web edge clamp 114 acts verticallywith no lateral or longitudinal disturbance of the web.

As has been made clear, it is necessary to rotate support/cooling tubes142. Rotation link 111 acting through cooling tube clamps 105 causessupport/cooling tubes 142 to rotate 60° during opening cycle, dumpingany ablation debris into a pan (not shown) located between the supportrails.

Calibration shims are located below the support plate 121. When thecalibration shim is removed, the entire assembly is lowered and thecalibration plate placed on top of the edge clamps.

Operation of table T has been fully described in copending patentapplication Ser. No. 08/536,748 filed simultaneously herewith on Sep.29, 1995 and incorporated herein by reference, entitled Apparatus andProcess for Holding Flexible Substrate, now pending.

In this reference the function of cylinder link 117, cylinder link 118,and pneumatic cylinder 119 together with front bell crank 112 and rearbell cranks 133 actuates a mechanical sequence of clamp, supporting,releasing, and debris dumping as ablation sequentially occurs. Thisapplication is incorporated by reference herein; detailed sequentialoperation of the apparatus will not be repeated here. However, thisreference is incorporated by reference as if fully set forth herein.

What is claimed is:
 1. A process for ablating a matrix of high density vias in a substrate comprising the steps of:providing a continuous flexible substrate; providing a mask having subapertures, which subapertures when scanned produce at a working distance from the mask an array of working images for ablating a corresponding array of vias in the substrate; providing a table for registering the substrate at the working distance from the mask; incrementally advancing and stopping the continuous flexible substrate over the table; providing a vacuum over the table and substrate; scanning the mask with coherent light to ablate the substrate over the table when the substrate is stopped to ablate the matrix of vias in the substrate in a vacuum; and, while maintaining the vacuum, removing debris from the table after the ablating step.
 2. A process for ablating a matrix of high density vias in a substrate according to claim 1 and wherein the step of:providing a continuous flexible substrate includes incrementally advancing a continuous flexible substrate from a supply roll to a take up roll.
 3. A process for ablating a matrix of high density vias in a substrate according to claim 1 and wherein the step of:removing debris from the table after the ablating step includes providing the table with a plurality of flat surface members; and, tilting the flat surface members after each ablation to discharge debris on the table.
 4. A process for ablating a matrix of high density vias in a substrate according to claim 1 and including the step of:cooling the table.
 5. A process for ablating a matrix of high density vias in a substrate according to claim 1 and wherein the step of:scanning the mask with coherent light includes scanning the mask with two beams of coherent light.
 6. A process for ablating a matrix of high density vias in a substrate according to claim 5 and wherein the step of:scanning the mask with coherent light includes alternating the two beams of coherent light. 